The present invention relates to an engine ignition system having interlocking apparatus for preventing the starting of the engine when such starting would be hazardous to the individual operating the engine.
Ignition systems with interlocks that prevent engine starting are not new in the art. Such interlocks are frequently used to prevent an individual from inadvertently injuring himself or someone else by placing the engine and associated equipment in operation. For example, small garden tractors have transmissions, clutches and attachments which may be left engaged when the engine is shut off. If the engine is started while the transmission, clutch or attachment is engaged, the tractor or its attachments could cause severe injury to the individual who starts the engine or someone standing nearby.
Any number of unsafe conditions may be monitored and used to control an ignition interlock. For example, a number of serially connected safety switches may be required to be closed before the interlock enables the ignition system. Each switch of the series may be associated with a given control member or other element which has an associated safe and unsafe starting condition. A clutch pedal may be required to be depressed, a transmission lever to be depressed, a transmission lever to be in neutral, a parking brake to be set, a seat belt to be fastened and a guard shield to be in place before the ignition system in enabled.
U.S. Pat. No. 3,726,265 issued to William A. Howard, discloses an ignition interlock of this type. The interlock prevents starting in the presence of an unsafe or hazardous condition by shorting out the magneto primary coil of a magneto system with an SCR in a conductive state. The safety switches must be in a closed position when the engine is started in order to render the SCR non-conductive and, hence, non-shorting. The SCR is held in a non-conductive state after the engine has been started and a safety switch is opened by a memory circuit which detects the pulses produced by the magneto primary coil. When the engine is shut off, the memory circuit in the absence of pulses allows the SCR to return to its conductive state inhibiting starting until the safety switches are again closed.
Since the ignition interlock is fundamentally a safety device, it should be fail-safe, that is, if any portion of the interlock is broken or fails to operate, engine starting should be inhibited. For example, if either side of the safety switch is grounded or if any wires in the interlock break, engine starting should not be possible. Also, an interlock is more economical to manufacture if it contains fewer electronic components. The adaptability of the interlock to systems other than a magneto system such as a CD ignition system is also desirable. In these respects, the present invention constitutes an improvement over that described in the above-identified patent.
Other advantages provided by the ignition system of the present invention include its adaptability to single or multi-cylinder engines, the ability to enclose the ignition transformer and interlock components in a single potted module, and the fact that the interlock requires no moving parts or engine modifications for use in an internal combustion engine.
Accordingly, it is a general object of the present invention to provide an ignition system with a safety interlock that constitutes an improvement over the prior art.